Stockers generally are installed within a semiconductor facility for temporarily storing workpieces, such as wafers, flat panel displays, LCD, photolithography reticles, or masks.
In the process of manufacturing semiconductor devices, LCD panels, and others, there are hundreds of processing equipments and thus hundreds of manufacturing steps. It is very difficult for the flow of the wafers, flat panels, or LCDs (hereafter workpiece) to be uniform from step to step, from tool to tool. Despite the best planners, there is always the unexpected scenario, such as a tool down, an emergency lot coming through, a periodic maintenance lasting longer than planned, thus there are various accumulations of the workpieces at certain steps for certain tools. The accumulated workpieces will need to be stored in a storage stocker, waiting to be processed.
Further, photolithography process is a critical process in the semiconductor fabrication facility, involving a large number of photolithography masks or reticles (hereinafter reticle). The reticles thus are typically stored in a storage stocker, and being retrieved when needed into the lithography exposure equipment.
The storage of workpieces and reticles (hereafter articles) is much more complicated due to the requirement of cleanliness. Damages to the articles can be physical damages in the form of particles, or chemical damages, in the form of interactions. With the critical dimension of the semiconductor device processing surpassing 0.1 micron, particles of 0.1 micron size, and reactive species will need to be prevented from approaching the articles. The storage areas typically would need to be even cleaner than the processing facility, to ensure less cleaning between processing.
Thus the stocker storage areas is typically designed to be sealed off from the outside environment, preferably with constant purging, and even with inert gas flow to prevent possible chemical reactions. Access to the storage areas is load-locked, to ensure isolation between the clean storage environment and the outside environment.
This creates a potential problem in the event of the failure of the stocker, such as a transport malfunction, or a load lock malfunction, the stocker storage becomes isolated, with no way to retrieve articles from the stocker storage. This failure, through the chain reaction, could shut down a large portion of the fabrication facility.